ly needed to accurately assess the solubilities of
As this review has shown, many factors with
the sulfate, bicarbonate and carbonate salts of Ca,
complex interactions contribute to the differential
Mg, K and Na at subzero temperatures before
movement of water and solutes in freezing soils.
these constituents can be accurately integrated into
Because of the complexity of solute-freezing phen-
geochemical models and ultimately into soil phys-
omena, modeling is an ideal approach for quanti-
fying these relationships. However, quantifying
icalchemical models.
aqueous-solute properties at subzero temperatures
Leung and Carmichael (1984) developed a
poses many experimental difficulties. As a conse-
model to describe solute partitioning between
quence, our ability to model these systems is fre-
water and ice during freezing. This model can be
quently limited by lack of basic data. The models
used to estimate partition coefficients from exper-
reviewed in this section, however, do indicate that
imental data. Working with slurries, Hanley and
significant progress has been made in the past dec-
Rao (1982) developed a model based on freezing
ade, which bodes well for the future.
potentials that takes into account the diffusion of
cations in the unfrozen portion of the sample, the
separation of ions at the freezing front, and the
RECOMMENDATIONS
migration of moisture and ions towards the freez-
Much research in cold regions is ultimately
ing front.
prompted by a quest for solving practical problems.
Several models have been developed that
Five major problems of cold regions associated with
describe the dynamics of freezethaw processes
freezing and thawing are soil strength, frost heav-
and solute redistribution in soils. Mahar et al.
ing, revegetation of severely disturbed lands, glo-
(1983) incorporated solute effects into a variation
bal carbon balance and contaminant transport. This
of the "Guymon" model to describe freezing of
review has identified several important aspects of
saline soils. They demonstrated that analytical
chemistry and freezingthawing processes that
modeling of freezing front penetration underpre-
impact on these problems.
dicts the rate of freezing when no account is made
Chemical thermodynamic equilibria of aque-
for the effects of salinity. They also found that the
ous electrolyte solutions at subzero tempera-
rate of advance to a given depth of freezing in-
tures are poorly understood. This is especially
creased with increasing salinity; they attributed
true of the solubilities of Ca, Mg, K and Na
this to the gradual release of the latent heat of fu-
sulfates, bicarbonates and carbonates, impor-
sion over a range of temperatures and depths due
tant salts in many saline soils and seawater.
to changing solute concentrations. Osterkamp
Chemical activities and mineral solubilities
(1987) developed an analytical solution for freez-
play a fundamental role in controlling the
ing and thawing of soils containing water or
chemical potential of water and ice in soils, the
brines. This model used empirical data on seawa-
freezing-point depression and the unfrozen
ter brine concentration as a function of tempera-
water content, which, in turn, play important
ture to parameterize the model. Osterkamp (1987)
roles in controlling the fluxes of water and sol-
found that maximum ice penetration is greater in
utes in soils.
the present of brines, which is similar to findings
There are strong and complex interactions
of Mahar et al. (1983).
among soil properties that control solute and
Kadlec et al. (1988) developed a mathematical
water flows along concentration, temperature
model to describe the solute segregation process
and hydrostatic gradients in freezing and fro-
at the freezing front and solute transport in the
zen soils. These complex interactions necessi-
unfrozen water of peatlands. This model demon-
tate the development of computer simulation
strated the downward movement of solutes,
which is important for establishing the geochro-
models that can integrate physical and chemi-
nology of deposits and determining the nature of
cal properties and processes. The ultimate goal
pollutant burial. Cary (1987) developed a numer-
is to develop models that can accurately ad-
ical model for calculating frost heave that couples
dress practical problems such as soil strength,
flows of heat, water and solutes as unsaturated
frost heaving and contaminant transport in
soils freeze. This model demonstrated, as noted
freezing and frozen soils.
previously under Frost heaving, that increasing
Does the freezethaw process significantly al-
ter soil gas (O2, CO2, N2O, CH4) concentra-
solutes can decrease frost heaving by reducing
tions? This has important ramifications for car-
water flows to ice lenses. To my knowledge, this
bon and nitrogen balance; nutrient availability;
is the only frost heaving model that explicitly in-
microbial, enzymatic and plant activity; soil
cludes solute effects.
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